Sunlight. Without it we wilt, like delicate little flowers. Yet cramped modern office life usually means someone will be cranking away at spreadsheets from a dark, windowless corner, which we already know is bad for mental and physical well-being.

We’ve seen studies linking too little daylight and depression before. But new research from a team of scientists in Brazil found further evidence that a lack of exposure to natural sunlight in work environments could be associated with physiological, sleep, and depressive symptoms.

For this study, researchers evaluated 20 women in a workspace for a week. Half of them worked near a window. The other half did not.

Researchers asked all the participants to wear a special activity watch (Philips’ Actiwatch 2, specifically), which monitors the amount of sunlight someone receives, as well as how active they are. For seven days, researchers tested their melatonin and cortisol levels (hormones associated with the sleep cycle and stress, respectively) from saliva samples. Along the way, they were also administered sleep-quality assessment tests and psychiatric evaluations.

Unsurprisingly, the “without window” group had higher cortisol levels by 10 p.m., which were “correlated with minor psychiatric disorders and depressive symptoms” in the evenings. The women working without daylight also had lower melatonin levels at night, which were associated with “depressive symptoms and poor quality of sleep.”

That’s ominous news that builds on a growing body of research that suggests sunlight is crucial for a healthy, well-balanced lifestyle. And since not everyone can have a corner office, it puts the onus on window-deprived workers to be proactive about upping their sunlight quotient. Consider it yet another reason to go for regular walks.